Start with what you know and fill in the factors:
Since the x^2 has a coefficient of 1, an x goes in each factor:
(x +- ?)(x +- ?)
Since the constant, 12, is positive, the signs in the factors are the same. Since the x term has a negative coefficient, both signs are minus:
(x - ?)(x - ?)
Now you need two factors of 12 which add to 7. The numbers 3 and 4 will work:
(x - 3)(x - 4)
Factors of 12 are 3 and 4.
Middle term is -7, which is -3 + -4, and munus times minus is plus, so
factors are (x-3)(x-4) = 0
x-values are 3 and 4.